The invention relates to a method for determining axle misalignment and tire wear of a vehicle by monitoring acceleration values on the vehicle.
Modern vehicles have several spaced axles each attached to wheels. Sometimes the axles become misaligned relative to each other. For efficient operation, vehicles require aligned axles. When axles are misaligned, the wheel do not face forwardly, but instead are at an angle relative to the drive direction. Misaligned axles can result in premature tire wear and reduce the efficiency of the vehicle.
The adjustment of the axle and wheels generally involves adjusting the steering axle, the forward drive axle, and the rear drive axle in order to allow the tires to contact the road or ground at a correct angle.
Presently, to determine whether and how much axle alignment adjustment is necessary, a worker estimates or makes a determination of the axle and wheel misalignment. Typically, this has been done while the vehicle is stationary by visually inspecting axles. If the operator of the vehicle does not seek to have the axle position tested, there is no simple way to identify misalignment.
Also, tire wear is potentially a problem. To date, tire wear has also been determined visually.
Although the above methods of determining axle misalignment and tire wear have been used for years, they are time consuming and sometimes inaccurate.
In the disclosed embodiment of the invention, a method of determining vehicle axle misalignment and/or predict tire wear includes monitoring values such as lateral acceleration and vertical acceleration values of an axle in motion. The data is stored and used to predict tire wear and determine axle misalignment.
Essentially, when an axle is misaligned, there will be a lateral acceleration applied to the wheels on that axle that would not be experienced by a wheel on a properly aligned axle. By monitoring those accelerations, one can make a prediction of how much misalignment there may be for a particular axle. Also, vertical acceleration values can help to make this determination more accurate. The lateral and vertical acceleration values can also be utilized to determine the amount of force that a tire may experience over time, relative to other tires. That is, if a tire is on an axle that is more misaligned than another axle, one can predict the tire will wear more rapidly. By storing this information one can make a prediction of undue tire wear for a particular tire.
Further, in a different aspect of this invention, if one is monitoring vertical acceleration one can predict tire wear relative to the tire wear on another tire. By identifying a normal tire wear, and by weighing the tire wear on each monitored tire to account for any undue wear due to excess weight or axle misalignment, this invention provides a method of identifying excessive tire wear that would predict when one tire may have worn more rapidly than the other tires on the vehicle.
This invention preferably monitors lateral and vertical acceleration over time on each axle. The mean of this data is then taken. A ratio of the mean lateral acceleration data of one axle divided by the mean lateral acceleration data of the other axle is then calculated. Preferably, the mean value is defined by dividing the sum of monitored values by the number of monitored values for a predetermined duration. This ratio of the means is multiplied a ratio of the same respective axle standard deviation of the vertical acceleration data. This final ratio, which is a product of the standard deviation ratio of the vertical acceleration data and the mean lateral acceleration ratio, is now a direct indication of the work done by lateral forces on the tires. If this final ratio approaches xe2x80x9c1.0xe2x80x9d the axles are more aligned. As the ratio of the data tends away from xe2x80x9c1.0xe2x80x9d the more misaligned the axles are. If they are perfectly aligned then the ratio should converge to xe2x80x9c1.0xe2x80x9d. The farther the ratio value is from the number xe2x80x9c1.0xe2x80x9d the more energy one axle is experiencing as compared to the other axle and therefore the more work done by the tires on that axle. If the ratio is higher than xe2x80x9c1.0xe2x80x9d it can be said that the first axle is xe2x80x9cmorexe2x80x9d out of alignment than the second. If the ratio is less than xe2x80x9c1.0xe2x80x9d it can be said that the second axle is more out of alignment than the first axle. If a threshold ratio value is exceeded a signal can be sent to the operator that the axles are out of alignment.
One can also experimentally determine tire wear by storing how bad the axles are misaligned over time. Again, a tire on an axle which is misaligned will tend to experience more wear. The amount of additional wear can be determined experimentally for a given amount of axial misalignment over a given distance and weight. The present invention can then predict tire wear for a tire on an axle having the sensed misalignment, weight and distance. One other way to predict tire wear of one axle as to another axle is to use the standard deviations of the vertical acceleration data alone.